The Great Irish Famine: What Was The Blight?
It's often said that "Those who cannot learn from history are doomed to repeat it" and the terrible Irish Potato Famine of the late 1840s is a lesson we've failed to completely take on board.
The potato, like the tomato, came to Europe from the Americas and initially was more of a curiosity than a crop. Eventually it developed into a staple food product, much as the grains (wheat and oats) are staples. In some ways the potato was a better food crop, especially for the poor. Easy to grow even on poor soils, less vulnerable to bad weather conditions and requiring less effort to turn into edible food it's popularity grew quickly. The boiled potato also contains more protein than bread and is actually a reasonably good source of vitamins, especially vitamin C.
Although not everyone was totally dependent on the potato, by the 1800's it was such a proportion of the general food supply that there was not enough slack in the system to cope with its withdrawal. There just weren't the reserves of other foods available.
The blight is thought to have come over on a ship from South America where the potato itself originated and in Ireland and Europe found the perfect conditions to spread. The blight is caused by a mould like organism called Phytophthora infestans. It spreads both by contact and in the air when weather conditions are right.
To develop the blight requires warmth and humidity, not rare in the summers of western Europe and Ireland. The weather is actually used to predict when blight will arise by looking out for Smith Periods, A Smith Period is a 48 hour period in which the minimum temperature is 10°C or more and the relative humidity exceeds 90% for at least 11 hours during the first 24 hours and for at least 11 hours again during the final 24 hours. However, any period of warm, humid weather increases blight risk.
Once the blight had infected a plant, it would typically kill it within 48 hours and have spread to neighbouring fields. The spores would also have travelled down the stem to the tubers and be lying on the soil.
The first reaction of the farmer was to harvest what crop he could which is where the real horror of the blight became apparent. Even crops that appeared untouched would have the spores on them and would begin to rot in store. When mixed with healthy tubers the disease would spread in store and turn the whole crop into a stinking inedible slush. Incidentally, the smell of blight is unmistakeable once experienced.
Even worse in some ways was late blight, where the plant would appear only mildly affected but the spores were lying in wait for the crop, striking when the farmer thought it was safely stored away. Whilst the Irish Potato Famine is well known, what many do not realise is that the blight plague moved across the water to infect Scotland and England, then moving across to continental Europe causing hardship and malnutrition for millions more.
When the blight first struck nobody had a real understanding of its cause and what treatments, or more accurately mitigating actions, were available but the real cause of the absolute devastation of the crop was the lack of genetic diversity.
It's well known today that some varieties of potato are more susceptible than others to the blight. We have some 400 varieties available to the grower and the latest varieties from the Hungarian Sarpo strain (Axona, Mira etc) are very resistant.
Sadly in those days there were only a few varieties being grown and none had any real resistance. If they'd had dozens of varieties under cultivation then the chances are that one would have been relatively unaffected.
Just as with the flu virus, there are different strains of blight to contend with, some more virulent than others and the organism mutates frequently. Different strains of the blight can develop and a variety of potato that is effectively immune today may well be susceptible next year to another mutation of the blight.
The lessons of the blight famine in food production are:
- not to rely on a small number of varieties of any crop
- not to allow one crop to have too high a share of the total
- to maintain a strategic reserve.
In the west we think of famine as thing of our past that now only affects the developing world yet we are not immune to the threat. Economic pressures and expectation of reliable supplies have reduced if not eliminated government provision of strategic foodstocks.
The just in time delivery chains of major food retailers have also reduced the slack and reserve that used to be in the system, most supermarkets' distribution chains now have only a few days supply in the pipeline.
Our chemical arsenals for dealing with crop disease are far better than those we had a hundred years ago but still potato cops were lost to a mutated strain of blight two years ago, despite multiple sprayings with fungicides. It's obvious that we still need the genetic diversity of multiple varieties but the pressure on farmers is always to grow the most profitable variety. Remember this does not only apply to potatoes, wheat and grains, soya and rice are all subject to the same pressures in the global market.
If we lost the potato crop today, then people would starve. Probably not in the affluent west but in the developing countries. If we lost wheat though, then the story would be different, even in the west we'd face serious problems.
They say every society is just three missing meals away from revolution, perhaps we should remember the lesson of the Irish Potato Famine before it's too late.
John Harrison lives in Crewe with his wife Val. He has written four books (published by Constable & Robinson) on Allotment Farming and Gardening. He and his wife are self-sufficient in vegetables and Val produces quantities of jams, chutneys and preserves from the produce. They maintain a website called Allotment Vegetable Growing.
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